Fuse construction



May 15, 1956 s. l. LINDELL 2,745,923

FUSE CONSTRUCTION Filed July 14, 1953 5 Sheets-Sheet 1 INV ENTOR.

May 15, 1956 s. l. LINDELL FUSE CONSTRUCTION 5 Sheets-Sheet 3 Filed July 14, 1953 y 1956 s. l. LINDELL 2,745,923

FUSE CONSTRUCTION Filed July 14, 1953 5 Sheets-Sheet 4 United States Patent FUSE coNsrnUoTIoN Sigurd I. Lindell, Chicago, Iii assignor to S & C Electric Company, Chicago, 11]., a corporation of Delaware Application July 14, 1953, Serial No. 367,801 29 Claims. (Ci. 29t)--116) This invention relates, generally, ing apparatus, and it has particular relation to dropout fuses. It constitutes an improvement over the dropout fuse construction disclosed in Lindell Patent No. 2,553,- 098, issued May 15, 1951, and assigned to the assignee of this application.

Among the objects of this invention are: To increase the interrupting capacity of a dropout fuse tube of the expulsion type; to accomplish this without increasing the size or strength of the fuse tube; to permit the fuse tube to move under restraint depending upon the severity of the fault that it is required to handle; to graduate the degree of restraint depending upon the extent of movement of the fuse tube which, in turn, is dependent upon the magnitude of the current to which the fuse tube is subjected; to employ two springs in series in order to provide two degrees of restraint, one spring being stronger than the other, together with fixed stop means to provide the final restraint; to back up the ferrule at the upper end of the fuse tube by the stronger of the two springs as the fuse tube recoils when a heavy fault current is interrupted, thereby reducing the stress in the fuse tube where the ferrule is anchored; to provide for sliding movement of the fuse tube to stress serially the springs to predetermined degrees of stress before further movement of the fuse tube is positively arrested; to maintain sliding contact engagement with the terminal assembly at the lower end of the fuse tube when the latter moves upwardly; and to provide a contact construction that requires a minimum of force to overcome friction between the moving parts and that assists in urging the fuse tube to swing to the open position.

Other objects of this invention will, in part, be obvious and in part appear hereinafter.

This invention is disclosed in the embodiment thereof shown in the accompanying drawings, and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of this invention, reference can be had to the following detailed description, taken together with the accompanying drawings, in which:

Figure 1 is a perspective view of a dropout fuse construction in which the present invention is incorporated;

Figure 2 is a vertical sectional view, at an enlarged scale, showing in greater detail the construction of the upper terminal member for the dropout fuse shown in Figure 1;

Figure 3 is a view, similar to Figure relative positions of the parts of the member when the fuse tube is removed;

Figure 4 is a vertical longitudinal sectional view showing the details of construction of the fuse tube and certain details of construction of the upper and lower terminal assemblies thereon;

Figure 5 is a view, in side elevation, showing the functioning of the weaker of the two springs in resisting the recoil of the fuse tube in an upward direction when the device is called upon to interrupt a relatively to circuit interrupt- 2, showing the upper terminal 2,745,923 Patented May 15, 1956 See light fault current and the operation of the sliding contact construction at the lower end of the fuse tube;

Figure 6 is a view similar to Figure 5, but showing the second spring means brought into action when the device is required to interrupt the flow of a somewhat larger fault current but not the largest that the device is capable of interrupting, the sliding contact being maintained; and

Figure 7 is a view similar to Figures 5 and 6 but showing the two springs fully stressed and the action of the stop means on the lower terminal member to arrest positively further upward movement of the fuse tube when it is called upon to interrupt the flow of current which is the maximum amount to which the device can be subjected and still properly interrupt the circuit.

Referring now particularly to Figure 1 of the drawings, it will be observed that the reference character 9 designates a support bracket which constitutes one of a pair of brackets that is employed for mounting devices on a cross arm carried at the upper end of a pole that is employed for supporting an electrical transmission line. The support bracket 9 is arranged to carry an insulator mounting as indicated, generally, at 10 which may be of the type shown in Baker Patent No. 2,606,954, issued August 12, 1952, and assigned to the assignee of this application. It will be understood, however, that other insulator mountings can be employed in practicing the present invention. The insulator mounting 10 includes a rearwardly extending support arm 11 which is secured, as shown, to the lower forwardly extending portion of the support bracket 9. Upper and lower metallic terminal supports 13 and 14- are provided, as shown, at the upper and lower ends of the insulator 12. It will be observed that the metallic terminal supports 13 and 14 extend forwardly of the insulator 12 which, preferably, is formed of porcelain.

The present invention has to do particularly with the dropout fuse mechanism that is mounted on the terminal supports 13 and 14. It will be observed that these terminal supports carry, respectively, upper and lower terminal members 15 and 16 and a fuse tube that is indicated, generally, at 17. In accordance with conventional practice the fuse tube 17 is removable. At its lower end it is provided with a lower terminal assembly, shown generally at 18, that is pivotally and slidably mounted on the lower terminal member 16. At its upper end the fuse tube 17 has an upper terminal assembly, shown generally at 19, which cooperates with the upper terminal member 15.

The lower terminal member 16 comprises a hinge casting 22 that is formed of suitable good conducting metal, such as brass, and has an inverted U shape. It is secured by a bolt 23 to the terminal support 14 at the lower end of the insulator 12. A split bolt connector 24 extends rearwardly from the hinge casting 22 and serves to receive a line conductor. At the opposite end of the hinge casting 22, slots 25 are provided in the opposite sides for slidably and pivotally receiving trunnions 26 that extend from opposite sides of a toggle member 27 through which a shaft 28 extends. The toggle member 27 is preferably formed of a brass casting and a more detailed description of its construction and operation is set forth in the Lindell patent above referred to. The toggle member 27 is pivotally secured by a hinge pin 29 to arms 3%! that extend rearwardly from a lower brass ferrule 31 which forms a part of the lower terminal assembly 18 and is provided on opposite sides with cylindrical contact surfaces 32, the center of which is indicated at 33, eccentric to the axis of the shaft 28. The function of this contact construction will be described hereinafter.

As shown more clearly in Figure 4 of the drawings, a

' toggle member 27 flipper 34 is rockably mounted on the shaft 28. As described in more detail in the Lindell patent, the flipper 34 is arranged to withdraw the flexible lead of a fuse link, to be referred to hereinafter, from the fuse tube 17 and also is arranged to keep the toggle linkage of which the toggle member 27 forms a part, in the operative position until the fuse link blows. For this latter purpose the flipper 34 has a shoulder 35 which is arranged to engage a shoulder 36 on a detent 37 that extends rearwardly from the lower ferrule 31.

Within the fuse tube 17, as shown in Figure 4, there is provided a fuse link 38 of conventional construction which has a flexible lead 39 extending therefrom and out of the lower end of the fuse tube 17. It will be observed that the lower end of the flexible lead 39 extends over the flipper 34- and, as long as the fuse link 38 remains intact, it serves to hold the flipper 34 in the position where the shoulder 35 engages the shoulder 36. The extreme lower end of the flexible lead 39 extends around a stud 40 and is clamped securely thereto by a clamp nut 41. The fuse tube 17, with the fuse link 38 interconnecting the terminal assemblies 18 and 19, constitutes an elongated conducting member pivoted on the lower terminal member 16 and swingable into and out of engagement with the upper terminal member 15.

The toggle member 27 has an eye portion 42 that is arranged to receive a prong of a switch stick. The purpose of this is to facilitate the handling of the fuse tube 17 for removing it from the mounting and replacing the same.

With a view to positively limiting the upward movement of the fuse tube 17, when it is subjected to the high est fault current that the device is intended to clear, the toggle member 27 has integrally formed therewith shoulders 43 on opposite sides above the cylindrical contact surfaces 32 that are arranged, as shown more clearly in Figure 7 of the drawings, to engage with a pair of inwardly extending shoulders 44 that are formed integrally with the hinge casting 22. As will be described in more detail hereinafter, when the recoil applied to the fuse tube 17 to move the same upwardly is sufficient to cause it to move to the position shown in Figure 7, the shoulders 43 on the engage the lower edges of the shoulders 44 and prevent further upward movement. However, before the fuse tube 17 can move to the position shown in Figure 7, it is necessary that the force of the recoil overcome the downwardly biasing forces applied by two serially arranged springs in the form of a recoil bar 63 and a coil spring 71 which form a part of the upper terminal member 15. They will be described presently.

Contact engagement is maintained with the contact surfaces 32 by auxiliary contacts 45, formed of copper strips, which are backed up by auxiliary contact springs 46, formed of stainless steel strips. The contacts 45 and springs 46 are generally L-shaped, are nested together, as shown in Figures and 6, and are secured to the underside of the upper portion of the hinge casting 22. When the contact surfaces 32 are swung out of engagement with the contacts 45, the lower end of each bears in prestressed relation against the rear edge of the respective stop shoulder 48 formed integrally with and extending inwardly from the sides of the lower terminal rember 16. As the toggle member 27 moves upwardly along with the fuse tube 17, as shown in Figures 5, 6 and 7, the contact surfaces 32 slide upwardly along and in spring pressed contact engagement with the contacts 45, thereby maintaining the circuit between the lower terminal assembly 18 on the fuse tube 17 and the lower terminal member 16. Since the. center of the cylindrical contact surfaces 32 is located at 33 above the axis of the shaft 28 and this axis is within the imaginary cylinder including these cylindrical contact surfaces, the forces exerted by the contacts 45 and springs 46 bias the toggle member 27 in a clockwise direction and thereby assist in the dropout action of the fuse tube 17. Moreovenbecause of the eccentric relation between the center 33 and the shaft 28 as the toggle member 27 swings about the latter, the contact surfaces 32 recede from the contacts 45, the springs 46 are correspondingly less stressed and the frictional resistance between the contact surfaces 32 and the contacts is reduced. There is then a continuous reduction in the frictional resistance incident to opening of the dropout fuse that must be overcome insofar as the contacts 45 are concerned.

The upper terminal assembly 19 at the upper end of the fuse tube 17 includes a brass ferrule 49 which is secured thereto by transverse pins 49', Figure 2. An eye 50 extends from the ferrule 49 to receive the prong of the switch stick, previously referred to, for the purpose of manipulating the fuse tube 17 into or out of the closed position. Threaded on the upper end of the upper ferrule 49 is a cap 51 which has a convex head 52 that engages the underside of a seat 53 formed integrally in the lower arm of a U-shaped top contact 54. The top contact 54 is formed preferably of a strip of brass that is silverplated. For illustrative purposes, it is pointed out that the top contact 54 is formed of a brass strip having a total overall length of about 6 /2", a width of about 2", and a thickness of about A5". The seat 53 is formed so as to have line contact with the convex head 52, the line of contact being circular. The silverplated surface provides a corrosion resisting contact surface having a relatively low contact resistance. A top contact strip 55 is connected by rivets 56 to the upper arm of the top contact 54. At its rear end the contact strip 55 is positioned underneath a leg 57 of an L-shaped terminal pad 58 which, as shown in Figure l, carries a split bolt connector 59 for receiving the other line conductor. A bolt 60 ex tends through the leg 57 and the terminal supports 13 together with the contact strip 55 to hold these elements securely in position Preferably the top contact strip 55 is formed of commercial bronze and is of the same width as the top contact 54. It also is silverplated.

With a view to providing a relatively stiff spring for resisting the upward recoil of the fuse tube 17 when it is subjected to shock incident to the interruption of the flow of a relatively high fault current, there is provided a recoil bar 63 that is clamped by the bolt 60 to the terminal support 13. The recoil bar 63 extends forwardly in cantilever fashion over the upper end of the fuse tube 17 Preferably the recoil bar 63 is formed of magnetic material,

such as cold rolled steel. For illustrative purposes, it is pointed out that it may be about 6%" long, 1 /2" wide, and V thick. Near the outer end of the recoil bar 63, there is a tapped opening for receiving a hollow threaded bushing 64. As shown in Figures 2 and 3, the bushing 64 is screwed into the recoil bar 63 and a portion projects above it for receiving a lock nut 65. It will be apparent that the position of the bushing 64 is adjustable. Advantage is taken of this feature to take care of variations in the distance between the upper and lower terminal members 15 and 16 on the insulator 12 and between the lower and upper terminal assemblies on the fuse tube 17 It is desirable to interconnect the rearwardly extending arms of the U-shaped top contact 54. For this purpose a contact stud or guide member 66 is employed. It is formed of good conducting material, such as brass, and its upper end 67 extends through the upper arm of the top contact 54 and is headed over within a suitable opening in the forward end of the contact strip 55 as shown in Figure 2. The lower end 68 of the contact stud 66 extends below the central portion of the seat 53 and is headed over as shown. Surrounding the lower end of the contact stud 66 is a guide Washer 69 having a central raised portion '70 which overlies the upper side of the seat 53. The outer portion of the guide washer 69 serves as a seat for the lower end of a coil compression spring 71, which is disposed coaxially with the contact stud 66 located, as shown, so as to be coaxial with the vertical axis of fuse tube 17. The upper end of the coil compression spring '71 extends around the lower end of the hollow bushing 6 4 and bears against the underside of the outer end of the recoil bar 63. The coil compression spring 71 is held in prestressed condition by the contact stud 66 and can be readily further stressed as compared to the recoil bar 63 so that the initial upward movement of the fuse tube 17 acts first to compress further the spring 71 without causing any substantial upward movement of the outer end of the recoil bar 63. Where only relatively small fault current is required to be interrupted, only the coil compression spring 71 will be stressed to any appreciable extent. Thus the recoil bar 63 constitutes a relatively strong spring and the spring 71 is a relatively weak spring.

It will be observed that an L-shaped reinforcing bar or conducting bracket 72 is mounted on the underside of the recoil bar 63 and below the terminal support 13. The horizontal arm 73 of the reinforcing bar 72 extends underneath the terminal support 13 and is secured thereto by the bolt 60. The downwardly extending arm 74 of the reinforcing bar 72 extends parallel to the vertical axis of the fuse tube 17 and is positioned rearwardly thereof between it and the insulator 12. Under certain conditions it is desired that there be conjoint movement of the reinforcing bar 72 and the recoil bar 63. For this purpose a pin 75 is employed. It will be observed in Figure 2 that the upper end '76 of the pin 75 is secured to the recoil bar 63. The lower end 77 of the pin 75 projects downwardly through a clearance opening 78 in the horizontal arm 73 and is headed over so as to cause the arm 73 to move upwardly when this headed-over portion engages the underside of the arm 73.

At the lower end of the downwardly extending arm 74, there is provided a V-shaped guide, shown generally at 79. The guide 79 includes forwardly extending conducting arms 80, Figure 1, at the outer ends of which are rearwardly curved arms 81. The forwardly extending arms 60 serve to guide the upper ferrule 49 of the fuse tube 17 into proper position generally regardless of the direction from which force is applied to the eye 50 to swing the fuse tube 17 to the closed position so that the contact head 52 will register with the seat 53. Preferably the guide 79 is formed of good conducting material, such as brass, since it may be called upon to conduct current when the fuse tube 17 is moved out of the circuit closed position while it is carrying load current by an auxiliary circuit interrupter shunted between one of the conducting arms 80 and the upper terminal assembly 19 as described in more detail in Patent No. 2,671,142, granted March 2, 1954, on application Serial No. 362,891, a continuation of the copending application of Lindell, Serial No. 254,- 036, filed October 31, 1951, now abandoned and assigned to the assignee of this application.

In describing the operation of the fuse construction disclosed herein, it will be assumed first that the fuse link 38 is subjected to a relatively slight flow of fault current so that the upward recoil applied thereby to the fuse tube 17 is relatively slight. It will be understood that, when the fuse link 38 blows, the fuse tube 17 functions somewhat in the same manner as the barrel of a gun when a cartridge is fired at the closed end. Under these conditions there is a tendency for the gun barrel to move rearwardly as the projectile moves forwardly through the open end. The position of the bushing 64 is adjusted so that the clearance between its lower end and the upper side of the central raised portion 70 of the guide washer 69 is one-fourth inch in one embodiment of the invention. The clearance between the shoulders 43 on the toggle member 27 and the lower edges of the shoulders 44 is nine-sixteenths inch in this embodiment when the trunnions 26' occupy the lower ends of the slots 25.

As soon as the fuse link 38 blows, the flexible lead 39 no longer is restrained and the toggle joint including the toggle member 27 no longer is held against movement. Also the flipper 34 is free to function for withdrawing the flexible lead 39 from the lower end of the fuse tube 17. This is accompanied by movement of the shoulder 35 away from theshoulder 36 to unlock the toggle. However, before any substantial movement of the toggle member 27 can take place, it and the fuse tube 17 move upwardly to an extent depending upon the degree of the recoil which, in turn, is a function of the severity of the fault that the device is called upon to interrupt. Under the assumed light fault current conditions, the fuse tube 17 moves upwardly together with the toggle member 27 an extent as indicated at 82 in Figure 5 of the drawings. As shown, the coil compression spring 71 is compressed a corresponding amount, its upper end being held substantially stationary against the underside of the recoil bar 63. It will be understood that the trunnions 26 move upwardly to the extent indicated at 82 from the lower ends of the slots 25 in the hinge casting 22. This movement will be one-fourth inch when the recoil is just sufficient to cause the guide washer 69 to engage the lower end of the bushing 64. F urther, it will be understood that this upward movement requires only a very short period of time during which only a slight movement of the flipper 34 takes place. Subsequently, after the recoil force has been dissipated, the trunnions 26 return to the lower ends of the slots 25. While this movement is taking place, the cylindrical contact surfaces 32 slide up the contacts 45. Subsequently, they swing away therefrom as previously described. The flipper 34 withdraws the remaining portion of the flexible lead 39 from the fuse tube 17 and the shoulder 35 moves out of engagement with the shoulder 36. This permits the toggle member 27 to rock about the shaft 28. Since the shoulder 36 no longer is restrained and since the toggle member 27 rotates in a clockwise direction, as viewed in Figure 4, the fuse tube 17 is lowered as the toggle member 27 pivots about the hinge pin 29. As a result the convex head 52 of the cap 51 is lowered out of engagement with the seat 53 and the fuse tube 17 then will swing about the shaft 28 to an open circuit position where it extends downwardly below the lower terminal member 16.

In the event that the flow of fault current is substantially greater than just described for the operation as illustrated in Figure 5, the upward recoil force on the fuse tube 17 is correspondingly more severe. Accordingly, the fuse tube 17 moves upwardly a distance indicated at 83 in Figure 6 where the trunnions 26 have moved this distance above the lower ends of the slots 25 in the hinge casting 22. The upper side of the central raised portion 76 of the guide washer 69 then engages the underside of the bushing 64 and thereby provides a direct connection to the recoil bar 63. The recoil bar 63 is moved from its position shown by broken lines in Figure 6 to its alternate position shown by full lines. This flexing movement of the recoil bar 63 to the alternate position requires the application of a substantially greater force than was required for compressing the coil compression spring 71 to the position shown in Figure 5. After the force of the recoil has been dissipated, the fuse tube 17 swings to the open position in the manner previously described.

Now, when the fuse tube 17 is subjected to extremely severe fault current conditions so that the fuse tube 17 is moved upwardly not only to compress the spring 71 but also to stress and flex the recoil bar 63 to a position beyond that shown by full lines in Figure 6, the fuse tube 17 will have moved upwardly a distance indicated at 34 in Figure 7 of the drawings. In the embodiment referred to, this movement is nine-sixteenths inch so that the outer end of the recoil bar 63 is flexed upwardly five-sixteenths inch. Here the trunnions 26 have moved away from the lower ends of the slots 25 to the extent indicated. This extreme upward movement of the fuse tube 17 is such as to cause the shoulders 43 on the toggle member 27 to engage the lower edges of the shoulders 44 that are formed integrally with the hinge casting 22. As a result further upward movement of the fuse tube 17 is positively arrested and yet it is held within the confines of the terminal members 15 and 16. Thereafter, the

fuse tube 17 moves downwardly until the trunnions 26 again are positioned at the bottoms of the slots 25 as shown in Figure l of the drawings. Then the fuse tube 17 drops out in the manner previously described.

It will be observed that the construction described is such as to withstand the various degrees of recoil which result from different degrees of blast action associated with are interruption. it will be observed also that the fuse tube 17 and the terminal assemblies 18 and B slide upwardly as illustrated in Figures 5, 6, and 7 of the drawings through various extents, depending upon the severity of the fault that is being interrupted. This movement involves three stages. The relatively light fault current is accompanied by an upward movement of the fuse tube 17 as illustrated in Figure 5, together with compression of the coil spring 71. When the recoil force is greater, the recoil bar 63 comes into play as shown in Figure 6. Where the force on the fuse tube 17 is even greater the recoil bar 63 is flexed and stressed as shown in Figure 7, together with the coil spring 71. In addition the horizontal arm 73 of the reinforcingbar 72 also is stressed and the shoulders 4-3 engage the lower edges of the shoulders 44 to positively arrest further upward movement of the fuse tube 17. By these combinations of actions, it is possible to interrupt considerably higher short circuit currents in the fuse tube 17 than would be possible if the conventional manner of restraint, principally at the lower end, were used. This is due to the fact that the fuse tube 17 with the restraint solely at the lower end places the fuse tube 17 in tension. Failure of such fuse tubes, closed at their upper ends, usually is not the result of radial bursting pressure on the inside of the fuse tube. Rather it is due to longitudinally applied forces incident to the sudden rise in pressure which tend to tear the upper ferrule 49 E of the fuse tube 17. In the construction disclosed herein where the restraint is to a large degree at the upper end, the tension applied to the fuse tube 17 is correspondingly reduced. In this way the fuse tube 17 is under relatively little tension stress and the strength thereof can be employed to resist bursting. It will be understood that the fuse tube 17, when highly stressed in tension, might also be ruptured because of this condition. As soon as the forces incident to the recoil have been dissipated, the fuse tube 17 returns to its lowermost position and then functions as a conventional dropout fuse to open the circuit.

It will be observed that the upper terminal member 15, including the U-shaped top contact 54, provides a relatively open design so that there is little likelihood that snow or ice will accumulate. Moreover, since the top contact 54 is somewhat flexible, any ice that might develop on its surface is readily cracked 06 as a result of change in position resulting from the upward recoil of the fuse tube 17.

In addition to providing a reaction against upward recoil, the coil compression spring 71 also provides contact pressure between the seat 53 and the convex head 52. This construction insures relatively high current carrying ability of the cutout without overheating at the contacts. Since the bushing 64 is adjustable in the recoil bar 63, it acts as a positioning member, for the upper terminal member 15. As pointed out this facilitates taking up variations in spacing between the upper end and lower terminal members and 16 which occur in 1nanufacturing operations.

Not only does the spring 71 insure that there will be good contact engagement between the seat 53 and the contact head 52, but also it insures that there will be a positive latching action between these two members which will hold the fuse tube 17 in the closed position.

The flow of relatively great fault current through the top contact strip 55 and the top contact 54 creates a magnetic field therearound which acts in a direction to increase the contact pressure between the seat 53 and the convex head 52 of the cap 51. The presence of the recoil bar of magnetic material increases the effectiveness of this magnetic field. Since the center of gravity of the U-shaped top contact 54 is within the space between the arms thereof, the magnetic forces tend to rock it in a clockwise direction as seen in Figure 2. This contributes to the mechanical resistance ofiered by the spring 71 and recoil bar 63 against the upward movement of the fuse tube 17 and finally by the shoulders 44.

Since certain changes can be made in the foregoing construction and different embodiments of the invention can be made without departing from the spirit and scope thereof, it is intended that all matters shown in the accompanying drawings and described hereinbefore, shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

l. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means being further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link, the extent of further stressing of said spring means depending upon the force exerted by the recoil, and stop means on said lower terminal member cooperating with said fuse tube to limit the upward movement thereof after said spring means has been stressed a predetermined extent and said fuse tube has been moved upwardly a predetermined distance.

2. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means comprising a pair of springs in series relation with one being substantially stronger than the other, the lesser strength spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube relative to the stronger spring, said fuse tube and said stronger spring moving upwardly conjointly when said recoil is suificient to overcome said lesser strength spring, and stop means on said lower terminal member cooperating with said fuse tube to limit the upward movement thereof after said stronger spring has been stressed a predetermined extent and it and said fuse tube have been moved upwardly a predetermined distance.

3. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppo-.

.pivot mounting on said lower sitely extending trunnions slidably and rockably mounted means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means being further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link, the extent of further stressing of said spring means depending upon the force exerted by the recoil, and stop means on said lower terminal member cooperating with said toggle member to limit the upward movement, thereof and of said fuse tube after said spring means has been stressed a predetermined extent and said fuse tube has been moved upwardly a predetermined distance, said U-shaped slots being of suflicient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid.

4. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said upper terminals member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its terminal member, said spring means comprising a pair of springs in series relation with one being substantially stronger than the other, the lesser strength spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube relative to the stronger spring, said fuse tube and said stronger spring moving upwardly conjointly when said recoil is sufficient to overcome said lesser strength spring, and stop means on said lower terminal member cooperating with said toggle member to limit the upward movement thereof and of said fuse tube after said stronger spring has been stressed a predetermined extent and it and said fuse tube have been moved upwardly a predetermined distance, said U-shaped slots being of sumcient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid.

5. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means being further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link, the extent of further stressing of said spring means depending upon the force exerted by the recoil, and stop means on said lower terminal member cooperating with said toggle member to limit the upward movement thereof and of said fuse tube after said spring means has been stressed a predetermined extent and said fuse tube has been moved upwardly a predetermined distance, said U-shaped slots being of sufficient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid, said stop means comprising a pair of inwardly extending shoulders in the path of movement of said toggle member and spaced above the same a distance equal to the distance said trunnions move away from the bottoms of said U-shaped slots.

6. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means comprising a pair of springs in series relation with one being substantially stronger than the other, the lesser strength spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube relative to the stronger spring, said fuse tube and said stronger spring moving upwardly conjointly when said recoil is sufficient to overcome said lesser strength spring, and stop means on said lower terminal member cooperating with said toggle member to limit the upward movement thereof and of said fuse tube after said stronger spring has been stressed a predetermined extent and it and said fuse tube have been moved upwardly a predetermined distance, said U-shaped slots being of sufiicient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid, said stop means comprising a pair of inwardly extending shoulders in the path of movement of said toggle member and spaced above the same a distance equal to the distance said trunnions move away from the bottoms of said U-shaped slots.

7. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said 11 fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufiicient to overcome said coil spring; and stop means on said lower terminal member cooperating with said fuse tube to limit the upward movement thereof after said recoil bar has been flexed upwardly a predetermined extent and its outer end and said fuse tube have been moved upwardly a predetermined distance.

8. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube form said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is suflicient to overcome said coil spring; and stop means on said lower terminal member cooperating with said toggle member to limit the upward movement thereof and of said fuse tube after said recoil bar has been flexed upwardly a predetermined extent and its outer end and said fuse tube have been moved upwardly a predetermined distance, said U-shaped slots being of sufficient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid.

9. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufiicient to overcome said coil spring; and stop means on said lower terminal member cooperating with said toggle'member to limit the upward movement 12 thereof and of said fuse tube after said recoil bar has been flexed upwardly a predetermined extent and its outer tendzand said fuse tube have been moved upwardly a predetermined distance, said U-shaped slots being of suificient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid.

10. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal membeer and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufficient to overcome said coil spring; a generally U-shaped top contact member having one arm interposed between the upper end of said fuse tube and the lower end of said coil spring and the other arm disposed above said recoil bar and connected to said upper terminal member, a stud extending through said recoil bar and said coil spring and interconnecting said arms of said U-shaped top contact member; said fuse tube, coil spring, and stud being coaxially disposed; and stop means on said lower terminal member cooperating with said fuse tube to limit the upward movement thereof after said recoil bar has been flexed upwardly a predetermined extent and its outer end and said fuse tube have been moved upwardly a predetermined distance.

11. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufficient to overcome said coil spring; a generally U-shaped top contact member having one arm interposed between the upper end of said fuse tube and the lower end of said coil spring and the other arm disposed above. said recoil bar and connected to said upper terminal member, a stud extending through said recoil bar and said coil spring and interconnecting said arms of said U-shaped top contact member; said fuse tube, coil spring, and stud being coaxially disposed; and stop means on said lower terminal member vcooperating with said toggle member to limit the upward movement thereof and of said fuse tube after said recoil bar has been flexed upwardly a predetermined extent and its outer end and said fuse tube have been moved upwardly a predetermined distance, said .U-shaped slots being of sufficient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid.

12. A circuit vinterrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said'upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly. against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufficient to overcome said coil spring; a generally U-shaped top contact member having one arm interposed between the upper end of said fuse tube and the lower end of said coil spring and the other arm disposed above said recoil bar and connected to said upper terminal member, a stud extending through said recoil bar and said coil spring and interconnecting said arms of said U-shaped top contact member; said fuse tube, coil spring, and stud being coaxially disposed; and stop means on said lower terminal member cooperating with said toggle member to limit the upward movement thereof and of said fuse tube after said recoil bar has been flexed upwardly a predetermined extent and its outer end and said fuse tube have been moved upwardly a predetermined distance, said U-shaped slots being of suflicient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid, said stop means comprising a pair of inwardly extending shoulders in the path of movement of said toggle member and spaced above the same a distance equal to the distance said trunnions move away from the bottoms of said U- shaped slots.

13. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said springmeans comprisinga recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressedon upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufiicient to overcome said coil spring; a generally U-shaped top contact member having one arm interposed between the upper end of said fuse tube and the lower end of said coil spring and the other arm disposed above said recoil bar and connected to said upper terminal member, and a stud extending through said recoil bar and said coil spring and interconnecting said arms of said U-shaped top contact member; said fuse tube, coil spring, and stud being coaxially disposed.

14. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, contact means carried by said lower terminal member, contact means on the lower end of said fuse tube slidably engaging said contact means on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means being further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link, the extent of further stressing of said spring means depending upon the force exerted by the recoil, and stop means on said lower terminal member cooperating with said fuse tube to limit the upward movement thereof after said spring means has been stressed a predetermined extent and said fuse tube has been moved upwardly a predetermined distance.

15. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member,- vertically extending spring strip contact means carried by said lower terminal member, cylindrical contact means on the lower end of said fuse tube slidably and rockably engaging said contact means on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means comprising a pair of springs in series relation with one being substantially stronger than the other, the lesser strength spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube relative to the stronger spring, said fuse tube and said stronger spring moving upwardly conjointly when said recoil is sufiicient to overcome said lesser strength spring, and stop means on said lower terminal member cooperating with said fuse tube to limit the upward movement thereof after said'stronger spring has been'stressed a predetermined extent and it and said fuse tube have been moved upwardly a predetermined distance.

16. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, a pair of vertically extending spring strip contacts carried by said lower terminal member and biased outwardly thereof, a pair of cylindrical contact surfaces on opposite sides of said toggle member slidably and rockably engaging said strip contacts, the center of said cylindrical contact surfaces being above the axis of rotation of said trunnions whereby the frictional resistance between said contact surfaces and said strip contacts decreases as said toggle member and fuse tube swing to the open position, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means being further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link, the extent of further stressing of said spring means depending upon the force exerted by the recoil, and stop means on said lower terminal member cooperating with said toggle member to limit the upward movement thereof and of said fuse tube after said spring means has been stressed a predetermined extent and said fuse tube has been moved upwardly a predetermined distance, said U-shaped slots being of sufficient depth to retain said trunnions therein while said toggle member is moved upwardly as aforesaid.

17. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar formed of magnetic mate rial secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufiicient to overcome said coil spring; a generally U-shaped top contact member having one arm interposed between the upper end of said fuse tube and the lower end of said coil spring and the other arm disposed above said recoil bar and connected to said upper terminal member, and a stud extending through said recoil bar and said coil spring and interconnecting said arms of said U-shaped top contact member; said fuse tube, coil spring, and stud being coaxially disposed; current flowing through said U-shaped top contact member creating a magnetic field the effect of which is increased by said recoil bar of magnetic material and which causes said top contact member to engage the upper end of said fuse tube with increased force.

18. A contact construction comprising, in combination, a support, a bar extending from said support, a U-shaped contact having the arms thereof coextensive with and on opposite sides of the end of said bar remote from said support, a guide member interconnecting said arms of said contact and extending through said end of said bar, and a coil compression spring interposed between one side of said bar and the inside of one of said arms.

19. A contact construction comprising, in combination, a support, a bar formed of magnetic material and extending from said support, a U-shaped contact having the arms thereof coextensive with and on opposite sides of the end of said bar remote from said support, a guide member interconnecting said arms of said contact and extending through said end of said bar, and a coil compression spring interposed between one side of said bar and the inside of one of said arms, current flowing through said U-shaped contact creating a magnetic field the effect of which is increased by said bar of magnetic material and which causes said one arm to move away from said bar.

20. A contact construction comprising, in combination, a support, a bar extending from said support, a U-shaped contact having the arms thereof coextensive with and on opposite sides of the end of said bar remote from said support, one of said arms having an exterior contact engaging surface, a guide member interconnecting said arms and guided onsaid one end of said bar, and a spring reacting between said bar and one of said arms to bias said one arm away from said bar.

21. A contact construction comprising, in combination, a support, a bar formed of magnetic material extending from said support, a U-shaped contact having the arms thereof coextensive'with and on opposite side of the end of said bar remote from said support, one of said arms having an exterior contact engaging surface, and being located substantially further away from said bar than the other arm, a guide member rigidly interconnecting said arms and guided on said one end of said bar, and a spring interposed between said bar and said one arm to bias the latter way from the former.

22. A contact construction comprising, in combination, a support, a bar formed of magnetic material extending from said support, a U-shaped contact having the arms thereof coextensive with and on opposite sides of the end of said bar remote from said support, one of said arms having an exterior contact engaging surface, and being located substantially further away from said bar than the other arm, an extension of conducting material from said other arm extending along said bar toward said support, a guide member rigidly interconnecting said arms and guided on said one end of said bar, and a spring interposed between said bar and said one arm to bias the latter away from the former.

23. A contact construction for the lower end of an expulsion fuse tube adapted to be latched in operative closed circuit position at its upper end comprising, in combination, a lower stationary terminal member, a toggle member adapted to be pivotally connected to the lower end of said fuse tube and pivotally mounted on said terminal member and arranged to be held in toggle locked position by a fuse link in said fuse tube to prevent movement thereof out of latched closed circuit position, said toggle member having'a cylindrical surface the center of curvature of which is above the pivot axis of said toggle member on said lower terminal member and said pivot axis is within the imaginary cylinder including said cylindrical surface, and spring means reacting against said cylindrical contact surface and biasing said toggle member to rock around said pivot axis when said toggle member is released on rupturing of said fuse link.

24. A contact construction for the lower end of an expulsion fuse tube adapted to be latched in operative closed circuit position at its upper end comprising, in combination, a lower stationary terminal member, a toggle member adapted to be pivotally connected to the lower end of said fuse tube and pivotally mounted on said terminal member and arranged to be held in toggle locked position by a fuse link in said fuse tube to prevent movement thereof out of latched closed circuit position, said toggle member having a pair of cylindrical surfaces on opposite sides the center of curvature of which is above the pivot axis of said toggle member on said lower terminal membet and said pivot axis is within the imaginary cylinder including said cylindrical surfaces, and a pair of spring members reacting between said lower terminal member and said cylindrical surfaces and biasing said toggle membet to rock around said pivot axis when it is released on rupturing of said fuse link.

25. A contact construction for the lower end of an expulsion fuse tube adapted to be latched in operative closed circuit position at its upper end comprising, in combination, a lower stationary terminal member, a toggle member adapted to be pivotally connected to the lower end of said fuse tube and pivotally mounted on said terminal member and arranged to be held in toggle locked position by a fuse link in said fuse tube to prevent movement thereof out of latched closed circuit position, said toggle member having a cylindrical contact surface the center of curvature of which is above the pivot axis of said toggle member of said lower terminal member and said pivot axis is within the imaginary cylinder including said cylindrical surface, contact means connected to said lower terminal member for engaging said cylindrical contact surface, spring means biasing said contact means into engagement with said cylindrical contact surface and thereby said toggle member to rock around said pivot axis when said toggle member is released on rupturing of said fuse link, and stop means limiting the movement of said spring means in the direction of said pivot axis whereby said spring means is prestresscd.

26. A contact construction for the lower end of an expulsion fuse tube adapted to be latched in operative closed circuit position at its upper end comprising, in combination, a lower stationary terminal member, a toggle member adapted to be pivotally connected to the lower end of said fuse tube and having a pair of oppositely extending trunnions for pivotally mounting it on said terminal member and arranged to be held in toggle locked position by a fuse link in said fuse tube to prevent movement thereof out of latched closed circuit position, said toggle member having a pair of cylindrical contact surfaces on opposite sides the center of curvature of which is above the axis of rotation of said trunnions and said pivot axis is within the imaginary cylinder including said cylindrical surfaces, a pair of spring pressed contacts carried by said lower terminal member and biased into engagement with said cylindrical contact surfaces to rock said toggle member around said axis of rotation of said trunnions when it is released on rupturing of said fuse link, and stop means limiting the movement of said spring pressed contacts in the direction of said contact surfaces whereby the same are prestressed.

27. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotally and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, and spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means comprising a pair of springs in series relation with one being substantially stronger than the other, the lesser strength spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube relative to the stronger spring, said fuse tube and said stronger spring moving upwardly ccnjointly when said recoil is sufficient to overcome said lesser strength spring.

28. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, said lower terminal member having a pair of generally U-shaped slots on opposite sides opening upwardly, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, a toggle member pivoted to the lower end of said fuse tube and having a pair of oppositely extending trunnions slidably and rockably mounted in said U-shaped slots, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, and spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member, said spring means comprising a pair of springs in series relation with one being substantially stronger than the other, the lesser strength spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube relative to the stronger spring, said fuse tube and said stronger spring moving upwardly conjointly when said recoil is sufficient to overcome said lesser strength spring.

29. A circuit interrupter comprising, in combination, upper and lower terminal members adapted to be held in fixed insulated spaced relation, a fuse tube adapted to receive a fuse link, said fuse tube being closed at its upper end and open at its lower end, means pivotaily and slidably mounting the lower end of said fuse tube on said lower terminal member, means latching the upper end of said fuse tube to said upper terminal member, means responsive to the blowing of said fuse link for releasing said upper end of said fuse tube from said upper terminal to swing downwardly to open circuit position, and spring means reacting between said upper terminal member and said fuse tube to bias the latter downwardly against its pivot mounting on said lower terminal member; said spring means comprising a recoil bar secured at one end to said upper terminal member and extending therefrom in cantilever fashion, and a coil compression spring interposed between the outer end of said recoil bar and the upper end of said fuse tube, said coil spring being first further stressed on upward movement of said fuse tube caused by recoil resulting from blowing of said fuse link and allowing movement of said fuse tube toward said recoil bar, said fuse tube and the outer end of said recoil bar moving upwardly conjointly when said recoil is sufficient to overcome said coil spring.

References Cited in the file of this patent UNITED STATES PATENTS 1,910,022 Legg May 23, 1933 2,183,083 Rawlins Dec. 12, 1939 2,212,632 Bodendieck Aug. 27, 1940 2,295,015 Schultz et a1. Sept. 8, 1942 2,324,114 Schultz et a1. -luly 13, 1943 2,328,818 Lindell et al. Sept. 7, 1943 2,331,848 Schultz Oct. 12, 1943 2,357,853 Smith Sept. 12, 1944 2,484,839 Lindell Oct. 18, 1949 2,553,098 Lindell May 15, 1951 2,574,400 Lesher Nov. 6, 1951 2,578,255 Lindell Dec. 11, 1951 2,611,054 Hubbard Sept. 16, 1952 2,623,919 Bowers Dec. 30, 1952 

